1. Field of the Invention
The present invention relates to annular vibration wave actuators including a vibration body and a movable body and configured to drive the movable body, and particularly relates to a shape of such a movable body.
2. Description of the Related Art
Conventionally, a vibration wave actuator configured to drive a movable body by vibration of a vibration body is known.
In such a vibration wave actuator, the vibration body typically includes an elastic body and a piezoelectric element as an electro-mechanical energy conversion element that is disposed on the elastic body.
The piezoelectric element having two driving phases at positions with a spatial phase difference of 90° therebetween is disposed on the elastic body, and two AC signals with a phase difference of 90° therebetween are applied to these two driving phases, whereby two bending vibrations are generated on the elastic body.
Then, a driving signal obtained by synthesizing these two bending vibrations shifts the movable body relative to the vibration body.
At least one of the vibration body and the movable body includes a friction member bonded, applied or formed at a contacting face thereof so as to produce an adequate friction force.
As driving by the actuator is repeated, this friction member becomes worn because the movable body slides to the vibration body. Therefore, the life of a vibration wave actuator can be lengthened by retarding such wear.
A contact surface pressure is confirmed as one of the factors deciding the wearing rate, and a smaller contact surface pressure can lengthen the life of a vibration wave actuator.
One of the methods of reducing such a contact surface pressure is to increase the area of a contacting portion.
Meanwhile, in order to avoid noise during driving, the contacting portion has to have elasticity.
To cope with these two matters, Japanese Patent No. 03049931 proposes a vibration wave actuator including a contacting portion formed with a beam-shaped member so as to support both ends of the contacting portion.